Noise is emerging as both an economic and public policy issue. Soundproof rooms are required for a variety of purposes. For example, apartments, hotels and schools all require rooms with walls, ceilings and floors that minimize the transmission of sound thereby to avoid annoying people in adjacent rooms. Soundproofing is particularly important in buildings adjacent to public transportation, such as highways, airports and railroad lines, as well as theaters, home theaters, music practice rooms, recording studios and others. One measure of the severity of the problem is the widespread emergence of city building ordinances that specify minimum Sound Transmission Class (“STC”) and Impact Insulation Class (IIC) ratings. Another measure is the broad emergence of litigation between homeowners and builders over the issue of unacceptable noise. To the detriment of the U.S. economy, both problems have resulted in major builders refusing to build homes, condos and apartments in certain municipalities; and in widespread cancellation of liability insurance for builders.
In the past, walls typically were made up of studs with drywall on both exterior surfaces of the studs and baffles or plates commonly placed between the studs in an attempt to reduce the transmission of sound from one room to the next. Unfortunately, even the best of such walls using standard drywall are capable of only reducing sound transmission by approximately 30 db, and much of that is focused on mid-range and high frequencies rather than lower frequencies which cause most of the complaints and litigation.
Various techniques and products have emerged to abate this problem, such as: replacement of wooden studs by steel studs; resilient channels to offset and isolate drywall panels from studs; mass-loaded vinyl barriers; cellulose sound-board; cellulose and fiberglass batt insulation; and techniques such as staggered-beam and double-beam construction. All help reduce the transmission of noise, but, again, not to such an extent that certain sounds (e.g., lower frequencies, high decibel) in a given room are prevented from being transmitted to an adjacent room, including rooms above or below. A brief review of commercially available products shows that there has been little innovation in these techniques and technologies for many years.
Floor/ceiling assemblies which are typically second floor, third floor, fourth floor have traditionally been constructed with gypsum wall board (GWB) or drywall on the ceiling below which is attached to a resilient channel (RC). The resilient channel could be attached to the joists, of the floor. These joists could be standard wood planks, trusses, wood I-beam, or other engineered joist system. The joists can range from a few inches to eighteen or twenty-four inches in depth. The space between the joists may or may not be filled with insulation. Traditionally a sub-floor is placed above the joists and a light-weight concrete or gypsum concrete material is poured on top of the sub-floor for acoustic and leveling reasons. The term light-weight concrete is used herein as a generic description for a concrete topping that is less dense than standard concrete. There are a number of significant disadvantages with light-weight concrete. Firstly, even though it is referred to as “light-weight” it is still very heavy, and you have to bring in separate sub-contractors. Secondly it leaves a lot of water in the building, which can cause mold which is a leading liability issue. Thirdly, while light-weight concrete helps to improve the STC rating it may often decrease the IIC rating. To counteract the IIC problem, a resilient acoustical underlayment is installed between the light-weight concrete and the subfloor. The underlayment is installed to reduce tapping noise from people walking across the floor. If underlayment is installed before the light-weight concrete is applied, the underlayment is extended up the walls to try to avoid getting the wet light-weight concrete on the installed drywall because it may cause mold. Then a second sub-floor is installed on the light-weight concrete and then a hardwood floor is installed over this second sub-floor. Thus a set of very complex operations have to be performed.
Accordingly, what is needed is a new floor/ceiling structure and a new floor/ceiling method of construction to reduce the transmission of sound from one room to an adjacent room.